Simultaneous Measurements of an Ultrasound and a Torsional Oscillator for 4He in a Nanoporous Glass

Previously, we carried out ultrasonic measurements for liquid ⁴He filled in a nanoporous glass (Gelsil), and observed an increase in the sound velocity due to decoupling of the superfluid component. At zero pressure, the superfluid transition temperature T _C is suppressed to 1.4 K from the bulk lambda point, 2.17 K. This behavior is the same as torsional oscillator measurements by Yamamoto et al. (Phys. Rev. Lett. 93:075302, 2004). However, the pressure dependence of T _C and the temperature dependence of the superfluid fraction are very different from the torsional oscillator measurements. In order to clarify the origin of the difference, we have developed a new technique of simultaneous measurement of an ultrasound and a torsional oscillator, and the system successfully works for a nanoporous glass. Here, we compare decoupling of the superfluid component for ⁴He films between an ultrasound and a torsional oscillator.     

基于扭转强迫振动风洞试验的矩形截面高层建筑三维风荷载研究

为了研究扭转振动对高层建筑三维气动力的影响,利用扭转强迫振动装置,通过多点测压风洞试验测试了三个矩形截面高层建筑模型在不同试验风速和不同扭转振幅情况的表面风压时程。进而讨论了结构顺风向、横风向和扭转向均方根风力系数及功率谱的变化规律,研究结果表明：结构顺风向、横风向和扭转向均方根风力系数均随着试验风速和扭转振幅的变化而变化;结构顺风向阻力系数随着扭转振动振幅的变化主要是由于结构顺风向气动力的变化引起,而其横风向和扭转向风力系数随着扭转振动的变化包含了气动力变化与结构气动弹性效应两部分。对于高层建筑来说,应考虑扭转振动引起的结构三维气动力的变化以及结构横风向和扭转向气弹效应。     

Evaluating the influence of pressure and torsional strain on processing by high-pressure torsion

Tests were conducted on an Al-6061 alloy to evaluate the separate effects of the applied pressure and the torsional straining in processing by high-pressure torsion (HPT). The values of the Vickers microhardness were measured after processing and plotted both linearly across the diameters of the disks and as three-dimensional representations. The measurements show that the applied pressure increases the hardness in the absence of torsional straining. In the presence of a pressure and torsional straining, the hardness values are high at the edges of the disk but lower in the central region. There is a gradual evolution toward a hardness homogeneity with increasing numbers of HPT revolutions. The hardness values at the edges of the disks are reasonably independent of the applied pressure but the extent of this region of high hardness depends upon both the applied pressure and the numbers of turns in the HPT processing.     

考虑涡旋效应的圆柱形TLD多维减震效果研究

调谐液体阻尼器可以控制地震作用下的结构动力响应。研究了利用圆柱形调液阻尼器来控制结构在地震作用下的扭转耦联振动。采用薄膜法建立了包含脉冲动压力和对流动压力的调谐液体阻尼器液动压力模型。基于准均匀涡旋理论获得了考虑调谐液体的抗扭力模型。建立了考虑偏心扭转效应的结构控制运动方程。以一装有调谐液体阻尼器的偏心结构为算例,对结构在地震作用下的扭转耦联减震效果进行研究,并分析了调谐液体的脉冲动压力、对流动压力和涡旋抗扭力在减震中的作用。结果表明：合理布置的调液阻尼器能有效控制结构的平-扭耦联振动,不能忽略液体涡旋产生的扭转力。     

The effect of hydrostatic pressure on the shear yield behaviour of polymers

The torsional stress-strain behaviour of isotropic poly(methylmethacrylate) (P M M A), poly(ethylene terephthalate) (P E T) and polyethylene has been studied under hydrostatic pressures up to 7 kbar. In P M M A the following important features were observed. First, there is a monotonic increase in the initial slope of the stress-strain curve with increasing pressure. Secondly, there is a substantial increase in the yield stress and the strain to yield as pressure is raised. Thirdly, there is a transition in the mode of failure at elevated pressure, the specimens fracturing in the high pressure region before a drop in stress occurs. Finally, in the high pressure region the fracture stress increases with increasing pressure but the strain at fracture decreases.The observed yield behaviour can be represented formally in a number of ways, and the results will therefore be discussed accordingly, in an attempt to give a general yield criterion for P M M A. The fracture behaviour has been analysed in terms of the Griffith ideas for fracture of glassy materials, and this will also be discussed.The results for poly(ethylene terephthalate) (Arnite) differ significantly from those for P M M A. Specimens of Arnite as received from the manufacturers were ductile in torsion at atmospheric pressure, and the torsional yield stress rose monotonically with increasing hydrostatic pressure. Annealing the specimens produced embrittlement at atmospheric pressure, but on testing under conditions where there is no tensile component of stress (i.e. at very low hydrostatic pressures) ductile behaviour was observed.The contrast between P M M A and Arnite suggests that in the former case there aresurface flaws which are penetrated by the hydraulic fluid at high pressures, whereas in the latter caseinternal flaws are produced by annealing.Polyethylene remained ductile over the complete pressure range, with a pressure dependence of the tensile yield stress which was similar to that shown by polyethylene terephthalate.1 bar=10⁵ N/m^–2     

诊断内燃机各缸作功均匀性的曲轴简谐扭振反算法

简要介绍了各种诊断内燃机各缸作功均匀性的方法及其局限性；依据内燃机动力学的基本理论，提出了一种利用轴系一个惯量的扭振信号多谐次分量反算内燃机各缸作功均匀性的新方法；详细推导和说明了该方法的基本原理；以某6L240柴油机为对象，进行了选用3个谐次的扭振简谐分量准确反算出各缸作功均匀性的仿真研究。理论分析和仿真研究表明．新方法只需以各缸停缸实验得到的扭振幅频特性参数为基础，利用一个惯量的扭振信号多谐次分量就可反算出内燃机各缸平均有效压力。方法简便准确，既不依靠轴系结构参数等较难获得的先验知识，又适用于内燃机轴系存在扭振的情况。     

Adiabatic shear banding in a thick-walled steel tube

We analyze the initiation and propagation of adiabatic shear bands in a thick-walled 4340 steel tube with a V-notch in the middle. The material is modeled as strain hardening, strain-rate hardening and thermal softening. The deformations are assumed to be locally adiabatic and the effect of inertia forces is considered. Two different loadings, i.e., torsional, and combined torsional and axial pressure are considered. In each case, the load generally increases linearly from zero to the final value, is kept steady there for some time, then decreases to zero and is kept at zero; thus a finite amount of energy is input into the body. For the combined loading, the magnitude of the torsional loading pulse is kept fixed and the effect of varying the magnitude of the axial pressure preload is investigated. A shear band first initiates in the element adjoining the notch tip and propagates radially inwards. By recording the time when a shear band initiates at the centroids of different elements we determine its speed of propagation in the radial direction to vary from approximately 50 m/s at the instant of its initiation in an element abutting the notch tip, to nearly 90 m/s by the time it reaches the innermost surface of the tube; the speed also depends upon the overall loading rate, and whether or not the loading is multiaxial. The drop in the torque required to twist the tube at the initiation of a shear band is not as sharp as that in a thin-walled steel tube. We compute the distance through which a shear band propagates as a function of the energy input into the body and thus ascertain the energy required to drive a shear band through a unit distance. We also study torsional deformations of a thick-walled CR-300 steel tube, model its thermal softening by a relation proposed by Zhou et al. and use material properties derived from their data. In this case, the speed of a shear band initiating from an element abutting the notch tip is found to vary between 750 m/s and 1,000 m/s at different points on a radial line through the notch tip; this agrees with that observed by Zhou et al. in their experiments on single-notched plates.     

六辊轧机扭振动态建模及与板带钢质量关系研究

考虑轧机扭振与辊系沿轴向动态特性和板带材质量的关系,基于连续体动力学建立了六辊轧机扭振动力学模型,包括轧机辊系等效模型和辊身与辊径过渡部分等效模型。根据轧制速度与轧辊角速度的关系,建立了板带钢前后张力、轧制力等参数与辊系扭振的关系模型。基于所建模型对某六辊轧机施加位移激励模拟扭振情况,仿真分析了轧机辊系和板带钢在扭振激励下的三维动态响应。仿真结果表明,轧辊角位移和角速度沿辊身长度方向波动较小;轧辊扭振使轧制压力、前张应力和后张应力横向分布发生不同程度的波动,扭振对前张应力分布影响较大,即对板带钢板形产生影响,且传动侧的波动幅值大于操作侧。     

On the stability of thin-walled, corrugated, circular cylindrical shells under external pressure

Summary Thin-walled, corrugated, circular cylindrical shells under external pressure have repeatedly buckled at much lower values than has been predicted from simple orthotropic shell theory, where a flexural mode of buckling is assumed, in-plane to the cross-section of the tube. In the present paper it is shown that there exists always a combined, torsional–flexural, out-of-plane mode of buckling, frequently corresponding to an extremely low critical pressure. The need to design these tubes also with respect to torsional stiffness is emphasized, and a formula for the buckling pressure is proposed. Dedicated to Professor Franz Ziegler on the occasion of his 70th birthday     

The corrosion behaviour of commercial purity titanium processed by high-pressure torsion

Commercial purity (CP) titanium was processed by high-pressure torsion (HPT) under an applied pressure of 6.0 GPa for different numbers of torsional revolutions and then exposed to a 3.5 % NaCl solution for open-circuit potential measurements followed by electrochemical impedance spectroscopy and potentiodynamic polarization tests. The electrochemical results exhibit a complicated relationship between the corrosion resistance and grain refinement. Thus, microhardness measurements reveal an improvement in hardness for CP titanium after processing by HPT but the corrosion resistance is lower in the NaCl solution than for the annealed coarse-grained Ti. It is shown that the corrosion susceptibility of the HPT-processed samples decreases with increasing torsional strain. The effect of grain size and microstructure on the corrosion properties of ultrafine-grained CP Ti is also examined.     

汽车传动系扭振引起的车内轰鸣声控制方法

某前置后驱微型客车存在低转速车内轰鸣声的问题,研究表明该轰鸣声由传动系扭振引起。首先对传动系扭振影响车内噪声的机理进行分析,在此基础上建立传动系扭振当量系统模型并进行自由振动计算。同时建立对象车型发动机仿真模型,从而获取发动机激振力矩,完成受迫振动计算。然后开展传动系扭振测试,并将自由振动及受迫振动计算结果与试验数据进行对比,验证了模型的有效性。然后利用此模型研究对象车型传动系扭振特性,从减小经后桥及后悬架向车身传递的扭振激励的角度出发,提出了一系列控制主减速器处扭振幅值的方案。试验结果表明所提方案对改善低转速车内轰鸣声效果明显。上述工作对解决同类问题具有一定意义。     

柔性复合材料前掠翼飞机静气动弹性分析

本文作者计算分析的是柔性复合材料前掠翼概念机的静气动弹性特性。文中作者利用NASTRAN计算了单独机翼的发散速度,并重点计算和分析了该机在亚音速情况下,飞行载荷和纵向静稳定性、操纵性导数分别随马赫数和动压变化的曲线。通过对比分析可以看出:(1)相同高度下,随着马赫数的增加,刚体纵向静稳定性、操纵性导数和弹性纵向静稳定性、操纵性导数分别呈不同的变化趋势,且某些变化相差甚大;机翼剪力、弯矩和扭矩随翼展变化的曲线中,刚体部分所占的比例不断减小,弹性部分所占的比例不断增加;机翼的最大垂直挠度(在翼尖前缘处)和最大扭角(在翼尖处)略有增加。(2)相同马赫数下,随着动压的不断增加,刚体纵向静稳定性、操纵性导数保持不变,弹性纵向静稳定性、操纵性导数呈线性变化;机翼剪力、弯矩和扭矩随翼展变化的曲线中,也同样是刚体部分所占的比例不断减小,弹性部分所占的比例不断增加;机翼的最大垂直挠度(在翼尖前缘处)和最大扭角(在翼尖处)略有增加。(3)使用复合材料剪裁技术可以适当减小机翼内洗,从而提高发散速度,减小机翼前缘垂直挠度和飞行载荷中弹性部分的比例。     

Effect of stacking sequence on the torsional stiffness of the composite drive shaft

Torsional stiffness is an important parameter judging the performance of composite drive shaft. In this paper, a new mechanical analytical solution of torsional stiffness for the composite drive shaft with balance laminate is derived based on classical lamination theory and mechanical analysis. Finite element analysis (FEA) has been used to calculate the torsional stiffness of carbon fiber-reinforced plastic (CFRP) drive shaft. A torsion test platform has also been constructed to measure the torsional stiffness of CFRP drive shaft specimens. Results of the mechanical analytical solution, FEA, and experiments show that the composite tube with the location of ±45° layers near to the outer surface is larger than the ones with the location of ±45° layers near to the inner surface. The effect of stacking sequence on torsional stiffness is larger in the thick-walled than that in the thin-walled composite drive shaft. The mechanical analytical solution can complement classical lamination theory which cannot reflect the effect of stacking sequence in calculating the torsional stiffness.     

Torsional vibrations of circular elastic plates with thickness steps

This paper presents a theoretical study of torsional vibrations in isotropic elastic plates. The exact solutions for torsional vibrations in circular and annular plates are first reviewed. Then, an approximate method is developed to analyze torsional vibrations of circular plates with thickness steps. The method is based on an approximate plate theory for torsional vibrations derived from the variational principle following Mindlin's series expansion method. Approximate solutions for the zeroth- and first-order torsional modes in the circular plate with one thickness step are presented. It is found that, within a narrow frequency range, the first-order torsional modes can be trapped in the inner region where the thickness exceeds that of the outer region. The mode shapes clearly show that both the displacement and the stress amplitudes decay exponentially away from the thickness step. The existence and the number of the trapped first-order torsional modes in a circular mesa on an infinite plate are determined as functions of the normalized geometric parameters, which may serve as a guide for designing distributed torsional-mode resonators for sensing applications. Comparisons between the theoretical predictions and experimental measurements show close agreements in the resonance frequencies of trapped torsional modes.     

Compensation of torsional vibrations in rods by piezoelectric actuation

In this paper, the piezoelectric compensation of torsional vibrations in rods caused by external excitations is studied. As an illustrative example, a laminated rod containing piezoelectric shear actuators is assumed to be fixed at the one end, and the other end is subjected to a torsional couple; additionally, a distributed torsional couple per unit length is acting. In such a system, cross-sectional warping is known to be present. The consideration of piezoelectric eigenstrains requires an extension of Saint Venant’s theory of torsion, which is achieved by introducing an additional warping function. Using D’Alembert’s principle, the boundary value problems for Saint Venant’s warping function, the additional warping function and the torsional angle are obtained. From the latter boundary value problems, the distribution of piezoelectric actuation is derived in order to completely compensate the external excitations, i.e. an analytical solution of the corresponding shape control problem is obtained. Finally, the results are verified by means of three-dimensional finite element computations.     

微纳米级键合强度分析(英文)

本文主要研究了微米/纳米尺度的键合技术和键合强度,给出并发展了基于MEMS技术的微米/纳米键合分析模型.为提取微米/纳米键合面积的最大剪应力和压应力,设计、制备和测试了一系列单晶硅悬臂梁结构.并使用理论公式和ANSYS有限元模拟对实验结果进行了分析.键合强度可以分为扭转和剪压表征两部分.根据测试值可得,最大抗扭强度为1.9×109μN.μm,最大压应力为68.3 MPa.     

Simultaneous Measurements of an Ultrasound and a Torsional Oscillator for Pressurized 4He in a Nanoporous Glass

Recently, torsional oscillator (Yamamoto et al. in Phys. Rev. Lett. 93:075302, 2004) and ultrasound (Kobayashi et al. in AIP Conf. Proc. 128:797, 2007) measurements were carried out for pressurized ⁴He filled in a nanoporous glass (Gelsil), and the superfluid transition temperature T _C shows a different pressure dependence. Thus motivated, we have performed simultaneous measurements with a torsional oscillator and with ultrasound for pressurized ⁴He in Gelsil. T _C is in agreement between the two techniques at all pressures, and the superfluid component above 0.5 K shows most of the same temperature dependence. Furthermore, it was found that the χ-factor (the fraction of superfluid which remains locked to the substrate ) is independent of measuring frequency between the torsional oscillator (kHz-order) and the ultrasound (MHz-order) ranges.     

复合型超声马达纵-扭振动固有频率简并研究

纵、扭振动固有频率简并是提高纵-扭复合型超声马达输出力矩的关键问题。然而同一弹性体内的纵振固有频率远高于扭振固有频率．目前对两种振动固有频率的简并缺乏深入的理论研究。纵一扭复合型超声马达振动分析模型都基于一维理论。在此提出了一种纵、扭振动固有频率简并的新方法。通过将纵一扭复合型超声马达设计成双定子对称结构．在定子上附加一个调整环改变定子的力学边界条件。实现纵、扭振动同频共振。应用Hamilton原理建立了考虑泊松效应的定子纵、扭振动理论模型，分析了定子的纵振与扭振第一阶固有频率随调整环质量和位置的变化规律，通过优化马达的几何结构参数获得了纵振与扭振的同频谐振点。     

直升机传动系统扭转振动的分析

为了获得直升机传动系统扭转振动的特性,对直升机传动系统的扭转振动进行了计算和分析.在简化传动系统结构的基础上,将直升机传动系统划分为若干个轴段和圆盘的子系统,根据振型叠加原理,得到了直升机传动系统扭转振动的解,分析了传动系统的扭转频响函数.结果表明:传动系统扭转频响函数幅值的峰值出现在低阶固有频率附近;不同频率激振源的部件引起传动系统同阶扭转共振时,发动机的转速不等,发动机到激振源部件的传动比大,发动机的转速高;在同阶扭转共振中,桨叶引起传动系统扭转共振时,发动机的转速最高.     

The effect of harmonic torque to torsional vibration of induction machines

Abstract

An increasing number of industrial control applications and home appliances employ power electronic devices which cause large concomitant harmonic currents. These harmonic currents distort the waveform of the voltage source and, in doing so, the distorted voltage can induce harmonic pulsating torque in the air gap and rotor harmonic torque of an induction machine. This harmonic pulsating torque generally causes torsional vibration. In addition, when the natural frequency of the mechanical system is in the proximity to the frequency of the rotor harmonic torque, the magnitude of the vibration becomes amplified and deteriorates rapidly; the torsional resonance occurs as well. In this investigation, we analyze the phenomena of torsional resonance caused by rotor harmonic torque and torsional vibration caused by harmonic pulsating torque.